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Objective. Spontaneous pneumomediastinum is a rare complication of dermatomyositis (DM) and polymyositis (PM).The aim of this study was to characterize this complication and determine its prognostic factors. Methods. We retrospectively collected a multicenter series of PM/DM cases complicated by pneumomediastinum. We analyzed all published cases and combined those that were exploitable with ours for an investigation of the factors associated with poor survival. Results. We collected 11 PM/DM cases complicated by interstitial lung disease and pneumomediastinum. Five of the 9 DM patients had clinically amyopathic DM without muscle weakness and high serum creatine kinase levels. The outcome was favorable in 7 of these patients and 6 had no sequelae. In total, ϳ25% of our patients of the 21 analyzable cases studied died within 1 month. With a median followup of 240 days, the cumulative estimated Kaplan-Meier survival rate was 64% at 1 year and 55% at 2 years. Poor survival was associated with absence of muscle weakness (P ‫؍‬ 0.02), initial low vital capacity (P ‫؍‬ 0.006), and initial low carbon monoxide diffusion capacity (P ‫؍‬ 0.04). Conclusion. In this first large series of patients with connective tissue disease complicated by pneumomediastinum to be reported, most patients had DM and half amyopathic DM, as in previous reports. Pneumomediastinum may occur before DM diagnosis and may thus reveal DM with minimal or no muscle involvement. Death was associated with an absence of muscle weakness and severe pulmonary involvement before the onset of pneumomediastinum. Corticosteroids and immunosuppressive therapy can result in complete recovery, as in half our cases.

ACPA-containing immune complexes induce TNFα secretion by blood and synovial fluid-derived macrophages from RA patients, fitting with their probable involvement in RA pathophysiology.

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